Many modern computers have a graphical user interface where the user operates a pointing device to move a pointer or cursor and to select target objects on a video display screen. A mouse is the most popular pointing device, but there are others, such as a trackball, touch pad, touchscreen, or joystick. But, all of these pointing devices require the user to use the hand or finger to press or click a physical or virtual button in order to select a target object (e.g. an icon, button, slider, link, or other object) on the screen. Some users have difficulty with this pressing operation because they have a physical disability that hampers their hand or finger motion or because their hands are otherwise occupied, such as a surgeon in an operating room.
To address this problem, hands-free pointing devices are available that may be mounted on a part of the body that the user is able to control, such as the head. The computer detects the position of the hands-free pointing device and when the head moves, the computer moves the associated cursor on the screen. The computer performs a selection operation (analogous to clicking a mouse) when the computer detects that the cursor has paused or dwelled on a target object for a specified time.
Unfortunately, if the specified time is set to be too short, users experience frustration by unintentionally selecting screen objects. Similarly, if the specified time is set to be too long, users experience frustration by being forced to maintain a steady head position directed at an object for a long time in order to select it.